Nicotine receptors in the substantia nigra are localized on dopamine cells in the zona compacta. The cholinergic input to the substantia nigra appears to originate from the peribrachial region. Nicotine-induced activation of locomotor behavior seems to be mediated through the mesolimbic dopamine system. The depressant effects of nicotine are mediated through the n. accumbens and thalamus. Nicotine receptors in the interpeduncular nucleus are localized predominantly on terminals of neurons originating from the habenula which may be cholinergic. Autoradiographic analyses indicate that the opiate antagonist cyclofoxy may be a valuable tool for visualizing opiate receptors using PET in humans. Male hamsters had higher binding of (3H)-naloxone in certain hypothalamic regions than females. No differences in the binding of (3H) D-Ala-D-leucine-enkephalin between males and females were found in the hypothalamus. Large sex differences in plasma beta-endorphin levels in hamsters were discovered under long-day photo periods. Beta-endorphin in plasma was also elevated in ovariectomized females but not changed in castrated males. Cyclofoxy was found to have anorectic properties. Chronic administration of morphine caused a suppression of the primary antibody response in vivo. This effect was probably mediated through T-cells or macrophages. Phencyclidine does not appear to activate dopaminergic nigrostriatal pathways. The effects of phencyclidine on locomotor asymmetries are probably determined through pathways projecting caudally from the substantia nigra.